Instruction manual

UltraLink 2 DVI Installation and Operation Manual 47
For example, to define the local address range 192.168.142.67 to 192.168.142.93, the smallest single block to
cover the range would be the 32 addresses from 192.168.142.64 to 192.168.142.95. The net mask needed to
accomplish this would be: 255.255.255.224. Consider the binary representation of this net mask:
11111111.11111111.11111111.11100000. Ignoring the first three octets, the final five zeroes of the mask
would ensure that the 32 addresses from 64 (01000000) to 95 (01011111) would be included in the range.
When specifying a mask, the user should not select values which will have ones following a zero in the
number’s binary form. For example, a net mask having 11100110 as the final octet is not advisable. The same
rule applies for each binary octet in the mask. For instance, if the third octet contains zeroes, the entire fourth
octet should be zeroes.
The mask values that should be used are listed below with the size of the address ranges they generate.
Mask
Octet
Binary
Equivalent
Size of
address range
255 11111111 1 address
254 11111110 2 addresses
252 11111100 4 addresses
248 11111000 8 addresses
240 11110000 16 addresses
224 11100000 32 addresses
192 11000000 64 addresses
128 10000000 128 addresses
0 00000000 256 addresses
Table 2. IP Access Control Net Masks
If it is not possible to adequately specify the desired address range with one IP address and one net mask, the
range can be broken down into two or more entries. Each of these entries could then use smaller ranges (of
differing sizes) that, when combined with the other entries, cover the required range.
For instance, to exactly encompass the address range in the earlier example, 192.168.142.67 to
192.168.142.93, the following six IP address and net mask entries could be added to the Access Control list.
Network/Address
Entry
Mask Entry Defined Address Range
192.168.142.67 255.255.255.255 defines 1 address (.67)
192.168.142.68 255.255.255.252 defines 4 addresses (.68 to .71)
192.168.142.72 255.255.255.248 defines 8 addresses (.72 to .79)
192.168.142.80 255.255.255.248 defines 8 addresses (.80 to .87)
192.168.142.88 255.255.255.252 defines 4 addresses (.88 to .92)
192.168.142.93 255.255.255.255 defines 1 address (.93)
Table 3. Sample Definition for IP Access Control Range
The same operation can also be accomplished by combining the Allow and Deny access values to form an
allowed or denied address range.